This invention is directed to preparing a steel mill waste material for use as metallic abrasives. More specifically, this invention is directed to a method for preparing scarfer spittings, a steel mill waste material, for use as size-graded metallic abrasives which can be used in machine or manual equipment to blast clean the surfaces of metals and non-metals and to the metallic abrasive so produced.
Scarfer spittings are a steel mill waste material produced by scarfing steel ingots, blooms, slabs, billets and bars prior to or during processing to remove surface defects. Scarfing consists of rapidly removing the surface of steel by the use of a fuel containing oxygen applied to the surface by means of a torch or torches. The oxygen oxidizes a portion of the steel thereby generating heat and increasing the temperature to cause the steel to become molten. The partially oxidized generally globular product is referred to as scarfer spittings. The scarfer spittings are cooled and flushed from the surface of the steel by high pressure water and are collected in a water bath. The scarfer spittings range in size from less than a #100 sieve size, that is, less than 0.149 mm to larger than 50.8 mm in diameter. The spittings are comprised of an outer shell of iron oxides surrounding an inner metallic core which has a chemical composition similar to that of the scarfed steel.
Scarfer spittings have no specific use. In recent years efforts have been directed to recycling the spittings in the steel mill to recover the iron which they contain. A portion of the spittings are mixed with mill scale, steel borings and the like and are used as part of the charge to a sinter strand to recover the iron. However, only the larger sized particles or spittings can be so used. Hence, most of the spittings must be removed from the mill and stored. In recent years, increased emphasis on the surface cleanliness of steel has resulted in an increase in the use of automatic scarfing machines to scarf the steel surfaces. As a result, the volume of scarfer spittings produced in a steel mill has increased, thereby increasing the time required to transport the spittings and the amount of storage space required for the spittings.
It is an object of this invention to provide a method for preparing scarfer spittings for a specific use whereby the problems of handling and storing of scarfer spittings in the steel mill are substantially reduced, if not completely eliminated.
It is the object of this invention to provide a method for preparing scarfer spittings comprised of inner metallic cores and outer brittle shells of iron oxides for use in machine or manual blast cleaning equipment to blast clean metallic and non-metallic surfaces.
It is another object of this invention to provide a product having a hardness of about R.sub.c 20 to 35 and a lathlike martensitic matrix which can be used as size-graded metallic abrasives having good toughness, extended service life and improved cleaning efficiency when compared with commercially available size-graded steel shot and grit abrasives.